1). Genetic linkage studies mapped a locus for hereditary prostate cancer, HPCX, to the long arm of the X chromosome at Xq27. The candidate region contains two clusters of SPANX genes, a SPANX-A/D subfamily including five members, SPANX-A1, SPANX-A2, SPANX-B, SPANX-C, and SPANX-D, and a SPANX-N subfamily including four members, SPANX-N1, SPANX-N2, SPANX-N3, and SPANX-N4, encoding cancer-testis specific antigens. Our previous analysis of the SPANX-B and SPANX-D loci identified several new DNA sequence variants resulted from gene conversion, though none of them was specific for X-linked families (Kouprina et al., 2005). During last fiscal year, we carried out mutational analysis of other SPANX genes (SPANX-A1, SPANX-A2, SPANX-C, SPANX-N1, SPANX-N2, SPANX-N3, and SPANX-N4) localized within the candidate region in the X-linked prostate cancer patients. Sequence analysis of the gene isolates did not reveal any alterations specific for the patients with hereditary prostate cancer. Thus, these and previous results indicate that either a specific combination of SPANX alleles or genomic rearrangements in the SPANX intergenic regions results in the predisposition to prostate cancer in X-linked families.2). Human artificial chromosomes (HACs) provide a unique opportunity to study kinetochore formation and to develop a new generation of vectors with potential in gene therapy. We constructed the first human artificial chromosome with a conditional centromere that can be inactivated by targeted modification of its epigenetic configuration in vivo. The HAC was built up using a DNA array based upon a synthetic alpha-satellite (alphoid) repeat containing one natural monomer, with a binding site for CENP-B (CENP-B box), and one completely synthetic monomer in which the region corresponding to the CENP-B box was replaced with a tetracycline operator (tetO). Binding of the tTA transcriptional transactivator dramatically destabilized the HAC, whilst expression of several other tetracycline-repression fusion proteins had no significant effect on HAC stability. The opportunity to selectively target different proteins into an active kinetochore and thereby regulate centromere function opens the way for an unprecedented mechanistic and structural analysis of the human kinetochore as well as for development of new HAC-based conditional gene expression systems.